The invention relates generally to power converters and more specifically to a system for driving electric machines connected to power converters.
The utility and importance of power conversion has grown with advantages being achieved in applications such as motor drives, renewable energy systems, and high voltage direct current (HVDC) systems, for example. The multilevel converter is emerging as a promising power conversion technology for various medium and high voltage applications.
Multilevel converters offer several advantages over conventional two-level converters. For example, the power quality and efficiency of the multilevel converter is better than that of the two level converter. Also, multilevel converters are ideal for interfacing between a grid and renewable energy sources such as photovoltaic (PV) cells, fuel cells, and wind turbines. Transformer-less multilevel converters have been designed using a modular structure. Such multilevel converters typically include a plurality of power modules that are coupled between DC buses. The modular structure of the converters allows stacking of these converters to provide different power and voltage levels.
Multilevel power converters typically include a plurality of semiconductor switches and energy storage devices that are placed between the input and output terminals. The semiconductor switches and energy storage devices in the converter aid in providing regulated output power at the output terminals. The output power at the output terminals is dependent on the activation of the semiconductor switches and energy present in the energy storage devices.
Some electric motors are coupled to output terminals of a power converter that is supplied with AC power and used to provide DC voltage. In conventional modular power converters, the energy stored in energy storage devices is dependent on the voltage and current on the AC side of the converter. This dependence leads to an increase in energy storage requirements.